Luffing crane



Jan. 30, 1940.

B. H. KERSTING ETIAL LUFFING CRANE Filed Feb. 25,1939

4 Sheets-Sheet 1 INVENTORS mam/1% yM Z'ZM Ja n. 30,1940- 5. H. KERSTINGET AL LUFFING CRANE 4 Sheets-sheaf 2 Filed Feb. 25, 1939 Jan. 30,

B. H. KERSTING ET AL.

LUFFING CRANE Filed Feb. 25,- 1939 4 Sheets-Sheet I5 J-.r IHZ 32INVENTORS Patented Jan. 1940 UNITED STATES PATENT OFFICE Coraopolis, Pasassignors to Dravo Corporation, a corporation of PennsylvaniaApplication February 25, 1939., Serial No. 258,534

9 Claims.

This invention consists in means for swinging pivotally mountedstructures; and, while it is of general applicability, we have developedit in application to the swinging of the jib of a crane,

and in such application we shall particularly describe it. The swingingin vertical plane of the jib of a crane is technically called luiiing.This lufling of the jib of 'a crane is commonly 'accomplishedby means ofpulley and cable. The

l0 means of this invention involvethe use of screw and nut. The objectsin vieware simplicity of structure and facility, speed, and accuracy ofoperation.

In the accompanying drawings Fig. I is a view I! in side elevation of agauntry crane of turret type mounted to travel upon' rails, in which thelufling means of our invention are employed; Fig. II is a view to largerscale and also in side elevation, showing fragmentarily the crane, and

showing in greater detail the lufling mechanism;

Fig. III is a fragmentary view, showing the luffing mechanism in plan;Figs. IV and V are views in ems-section, showing the luiiing mechanismto still larger scale on the planes respectively indicated at IV-IV andV-V, Fig. II; Figs. VI and VII are views in axial section and in endelevation of a certain nut and bearing assembly, and Fig. VIII is. aview partly in side elevation and partly in axial section of suchassemao Fig; IX is a fragmentary view, showing in axial section, onlarger scale than Figs. VI to and bearing assembly; and Fig. X is adiagrammatic view in side elevation 011a draw-bridge which includes apivotally mounted element,

and to which application is-made'of the swinging means of the invention.

The gauntry crane of Figs. I-VIII ,afiords example of the practice ofthe invention; the

invention is in no sense limited to this or any other particular form ortype of. crane; and, as is manifest on consideration of Fig. X, it is ofgeneral applicability in the swinging of pivotally mounted structures. k

The crane stands upon a base I (in this instance a platform mounted torotate turret-like upon a derrick 2). It includes a jib 3 pivoted to thebase at 4 and adapted to swing in vertical plane upon such pivotalmounting. Such swinging in vertical plane is, as has been said, termedlumng. From a drum 5 rotatably mounted in base I a hoist line Ii extendsthroughout the length of the jib and supports in a suitably formed.bight a block 1. Upon' this block the ll load is hung. It does notconcern us further (Cl. 21H) to describe details and refinements of loadcarry- .ing.'

The jib 3 of the crane will be seen to be a trussv structure, of generaltriangular outline, pivoted by'one comer of the triangle'upon the 5 baseI, and itself including a basal chord memher 8. This chord member 8 of.the arm" is pivotally connected at one end to the base I A thirdmember, ascrew 9, is through'intermediate parts presentlrtobe'described, pivoted at one in of its ends tothe distal end of thepivotally mounted member 8 (at point I0) and at its other end (throughintermediate parts) to base I at a point II, remote from pivot 4. Thebase I, the chord member 8, and the screw-9 thusform a It triangle(called in the industry an A frame). Of this triangle of members, theeffective length of one (the screw 9) is variable: and by, variation inthe effective length of this member the frame is swung and luiiing iseffected. 2o

The screw 9 is oppositely threaded at its two ends and can'ies upon itsoppositely threaded ends twp oppositely threaded nuts, I2 and. I3. Thenuts'are pivotally mounted; in pairs of links I4, I and I5, I5 that move.in a runway 25 in a frame I6, and in their mounting are secured againstrotation. These links are pivoted, one pair to arm 3 at III, the otherpair to base I at II. It is manifest, then, that as screw 9 is rotatedin one direction or the other and the '39 I pairs of links drawntogether or spread apart, VIII, the internally threaded portions of thenut the effective length of the screw as a member of the A frame isdiminishedor increased, and the arm 3 is swung upward or downward. The

positions illustrated in full lines .and inbroken .35 lines in Fig. Iindicate the shifting ofposition of the parts. The range of swing is notlimited to the positions shown,.but is of much wider extent.

The screw' 9 may be equipped with a gear- 40 wheel I1, and the frame I6with a motor I8, by

' which through suitable transmission mechanism rotation in desireddirection, at proper speed,

and to desired extent may be imparted powerfully to screw 9. The frameI6 is'assembled with the links I 4,

. I, I5, I5, and affords a floating runway and torsion-resisting memberfor the links and a sup port for the motor I8. structurally the frameincludes two-parallel beams I60. spaced apart r," and rigidly integratedwith cross-struts ISI. The screw .9 extends between the beams I60, andat opposite ends is journaled in bearing blocks. thatare secured.against. axial displacement,

by means of keepers I62 rigid with the frame. 5

The inner faces of the beams I60 carry longitudinal rails 26, upon whichthe links I I, I I and I5, I5, when assembled'with .the nuts, areadapted to travel. The structure holds the links (and the cups 23presently to be described) against rotation. The links include lateralprojections I II, II that are notched to engage the rails 26,

as shown in Fig. IV; and between the paired links the nuts I2 and I3 areseverally mounted. 4

Provision is made for the distribution of stress between nut and screw.The practical limitations upon the degree of perfection attainable inthe preparation of materials and-in the fabrication of parts give valueto this provision. The nut has gimbal mounting in the pairs of 7 links;and, accordingly, under stress transmitted between screw and link, thenut adjusts itself .upon the screw, and stress that might otherwise beconcentrated at one point is distributed around the circumference of theinterengaged threads. The gimbal mounting is found in a cylindrical cup23 with a bottom orifice through which in the assembly the screw 9extends, and within which the nut is arranged. Externally the cup isprovided with trunions 24 by which it is pivotally mounted in theassociated pair of links (I4, I4 or I5, I5)., Internally the. cup isprovided with transversely extending cylindrical bosses, convenientlyformed as pins 25 welded in orifices in thecup walls. The axes oftrunions 24 and of pins 25 are angularly displaced at a 90 angle,

immediately provided with the bearingsurfaces to engage the pins 25. Thetwo partsare united against relative rotation by the spline 22.

Upon the part 2| a supplementary nut 30 is mounted bybolts 3I-,- and by"such mounting is minutely adjustable in its position. The supplementarynut 30- is provided upon its outer face (the face that in the assemblyis remote from the nut 20, 2 I) with an outstanding diametricallyextending ridge 32 of a width less than the overall diameter of thescrew 9. The threads within the nut 20 are so proportioned as to fillthe complementary threads in the screw 9; the threads in thesupplementary nut 30 are so proportioned as toafford a small playbetween the opposed surfaces of the threads. When the parts areinitiallyassembled, the faces of the threads in nut 30, which-otherwisewould hear the stress of service,

. stand away from the thread on the screw 9. In

consequence, it is the nut 20 that primarily bears the stress ofservice. As in continued use the interergaging surfaces wear away, thespace narrows at which the thread surfaces of the supplementary nut 30stand apart from those of the screw. The narrowing of this space isvisible as through a window at the sides of the ridge 32; and thus atell-tale is provided, by which deter:

'mination may be made, when the nut 20 is so far worn as to requirereplacement.

Manifestly, it is only the reach of the screw 9 between the nuts I2 andI3 that is subject to the tension stresses of the load, and, of course,if the screw breaks, it will break at some point in the interval betweenthe nuts. In the event of such screw failure, the two ends of the screwseverally extending between the nuts I2 and I3 and the thrust blocks 90at the opposite ends of the frame I6, become compression members, andtransfer through the keepers I62 to the body of the frame I6 theload-sustaining tension, normally borne by the portion of the screwbetween the nuts. Thus, the frame I6, normally serving as a runway andmotor support, is adapted in emergency to be come the effectiveload-sustaining member, preventing undue harm to the apparatus, andserious danger to workmen.

The nuts 20 will normally be formed of bronze;

but the supplementary nuts 30, serving their described purposes, not oftell-tale merely, but, if

for any reason the threads in the bronze nuts 20 fail, of compressionmembers also, will advantageously be formed of steel of high shearstrength.

The screw is supported in the frame" by the nuts, and at the ends thereis suflicient normal clearance from blocks 90 to allow for wear betweenscrew and nuts.

The structure allows the screw to float in the nut assemblies I2 and I3,and, as has been said,

the stress is distributed over the engaging surfaces around thecircumference of the screw.

Already we have said that the screw 9 floats in the frame IS, in that itis mounted in blocks that have universal pivotal mounting in the frame.Furthermore, it will be observed that the frame I6- floats, in thesensethat, in addition to its pivotal movement upon points III and I I, ithas movement of longitudinal translation relatively to base I and arm 3.Such movement is indicated in the broken-line position, Fig. I.

The operation of lufiing is effected by rotation of screw 9 with theeffect that the pairs of links I4, I4 and I5, I5 are-drawn together orspread apart; the effective length of one arm of the A-frame isdiminished or increased; and arm 3 is raised or-lowered. In case thescrew 9 breaks under load, the frame I6, through the keepers I62,becomesthe tension member, sustaining the load.

shown, consisting of two halves '40 severally mounted pivotally uponopposed bridge-heads 50, and adapted to be swung severally fromfull-line to dotted-line positions. In this case also each bridge halfis in structure a truss that includes a chord member 80. Between thedistal end of chord 80"(the end remote from the point of pivoting) and apivot mounted on the bridgehead 50 at an interval from the pivotal pointI0 of the chord member 80, such a structure as that already shown anddescribed may be introduced. And, by means of such a structure, thedraw-bridge halves may be raisedand lowered.

Whereas the bridge illustrated consists in two pivotally mounted bridgesections that are 'adapt ed to be swung severally between horizontal andelevated positions, the art is familiar with draw In'Fig. X adraw-bridge is diagrammatically bridges that have a single member thatis adapted to be swung in vertical plane. Manifestly, the structure ofthe invention may be also employed in bridges-of this sort.

In like manner, as will be understood, the invention may be applied tothe swinging o f-the gates of locks in canals; and, generally, in theswinging of pivotally mounted structures.

We claim as our invention:

1. Means for swinging a structure" pivotally tation to effect thedrawing together of the nuts and of the carriages that bear them.

2. The structure of claim 1, the gimbal mountings including each a cupbeing pivotally mounted in one of said carriages on an axis transverseto the axis of the screw and each cup being additionallyadapted to bepivotally engaged by the nut on an axis of turning also transverse tothe screw axis and angularly displaced (with respect to the screw axisas a centre) from the axis of pivotal mounting first named.

3. In a crane structure including an arm in the form of a truss withbasal chord member, pivotally mounted at one end of such basal chordmember to an extended base, lufiing means,.including a frame withlongitudinally extending runway, two oppositely threadednuts mounted insaid runway, one of said nuts being pivotally connected to the basalchord member of 'said arm at a point remote from the point of pivotingto the said extended base, and the other of said nuts being pivoted tothe said extended base'at a point remote from the said point of thepivoting of the arm upon it, and a rotatable bolt formed with oppositelythreaded portions simultaneously engaging the two said nuts.

4. In a crane including an arm pivotally mounted upon a base, luflingmeans, including a frame with longitudinally extending runway-two linksadapted to travel in said runway, two nuts mounted with universalpivotal connection, one to each link, a screw extending longitudinallyof said frame and engaging the nuts in said links, one

of said links being pivotally connected to said arm at a point remotefrom the point of pivotal mounting upon the base ,and the other of saidcarriages being pivotally connected'to said base -at a point remote fromthe-point of pivotal mounting of the arm upon it.

5. In a crane including 'an arm pivotally mounted upon a base, luflingmeans, including a frame-with a, longitudinally extending runway, twolinks adapted to travel in said runway, two nuts mounted with universalpivotal connection, one to each link, a screw extending longitudinallyof said frame and engaging the nuts in said links,

one of said links being pivotally connected to said arm at 'a pointremote from the point of pivotal mounting upon the base, and the other Iof said links being pivotally connected to said base at a point remotefromthe point of pivotal mounting of the arm upon it, and means forrotating said shaft to vary the space interval between said links.

6. In a crane including an arm pivotally mounted upon a base, lufiingmeans, including a screw carrying two nuts connected, one to said arm ata point remote from the point of pivotal mounting upon the baseyand theother to the base at a point remote from the point of pivotal mountingof the arm upon it, and a floating frame borne by and providing runwayfor said nuts.

7. In a crane including an arm mounted upon a base, lufling means,including a frame with a longitudinally extending runway, two nutsadapted to travel in said runway, a screw extending longitudinally ofsaid frame and engaging the said nuts, one of said nuts being pivotallyconnected to the said arm at a point remote from the point of pivotalmounting upon the base, and the other of said nuts being pivotallyconnected to said base at a point remote to the pivotal mounting of thearm uponit, the said frame being provided with abutments beyond the twoends of said screw in such assembly,, whereby, in case of screw failure,the frame becomes, a tension member sustaining the load.

8. In a crane including an arm pivotally mounted upon a base, meansincluding a screw and a traveling nut for swinging said arm in verticalplane, anda frame including a runwayfor said traveling nut, said frame.carrying an abutment adapted, in case of screw failure, to be engaged bysaid screw and to transmit the load stress to said frame.

W 9. Means for swinging a, structure pivotally mounted upon a support,such means including a frame, two nuts rotatably borne by said frame andpivotally connected, one to the swinging structure and the other to thesupport, a screw simultaneously engaged by the two said nuts and adaptedon'rotation in one direction or the other to effect the drawing togetheror the recession of the nuts from one another, a prime mover borne bysaid frame, and rotation-imparting connection between said primemover-and said screw BERNARD H, KERSTING. HANS ENARD.

